The present invention relates to the diagnosis of deep venous thrombosis. More particularly, the invention relates to a high-sensitivity method and automated apparatus for the noninvasive exclusion of acute, proximal deep venous thrombosis in a significant percentage of those patients suspected of, but actually negative for, deep venous thrombosis.
Deep venous thrombosis (DVT) is a well-known clinical indication commonly occurring in post-operative patients, elderly persons and patients with severe debilitating illness or malignant diseases, especially malignancy of the pelvis or abdomen. It is a frequent cause of emergency admission to hospital and, particularly in the case of acute, proximal DVT, can result in pulmonary embolism (PE), which is often fatal. The treatment of DVT is known to most often involve the administration of anticoagulant therapy, which presents the risk of hemorrhage and, in pregnant women, poses hazard to the viability of the fetus. Consequently, it is generally accepted standard of care to obtain a reliable confirmation of DVT prior to beginning treatment.
In present investigative practice, venography is accepted as the gold standard for the clinical confirmation of DVT. Unfortunately, venography is invasive, involves the injection of radiographic contrast media and exposes the patient to ionizing radiation during the examination. While each of these factors militates away from the unnecessary utilization of venography, the injection of radiographic contrast media is of particular concern. These media are known for potentially fatal complications including anaphylaxis or anaphylactic reaction, bronchospasm, angioneurotic edema with laryngeal spasm or edema, severe hypotension with circulatory failure and cardiac arrhythmias or arrest. In addition, the physical injection of the contrast media poses the risk of actually causing a DVT to break loose, resulting in PE. In order to avoid the attendant risks of venography, Doppler ultrasound has been employed where available as a screening tool for the confirmation of some DVT, thereby eliminating the need for a percentage of venography examinations.
Unfortunately, Doppler ultrasound is operator dependent and somewhat subjective in interpretation. As a result, Doppler is not generally regarded as reliable for the exclusion of DVT. Therefore, in the case of negative Doppler results, it is still necessary to perform venography for the exclusion of DVT. To compound this deficiency, Doppler equipment and trained operators are not readily available and where available are in very high demand. Recognizing the hazards of venography and the limitations of Doppler, researchers have recently focused effort on the development of efficient screening means for the exclusion of DVT. The general theory is that if a percentage of patients suspected of DVT can be reliably excluded from the indication then more Doppler resources will be available for the confirmation of DVT. The desired net result is that venography will only be necessary in that percentage of cases that cannot be reliably excluded or confirmed by other available means.
From these efforts, thermography and, in particular, infrared (IR) imaging has emerged as a promising technique, offering the advantages of high sensitivity and relative low cost through a noninvasive method. In general, thermography involves the thermal mapping of the suspected DVT positive patient""s lower extremity and evaluation of the resulting thermogram for known indications, or more precisely the lack thereof, of DVT. The method relies primarily on two known observables. First, the thermogram obtained from a DVT negative subject will exhibit a generally smooth temperature gradient of approximately 3xc2x0 C. between the upper thigh and the lower calf. Second, there is no significant contralateral asymmetry in the thermograms of a DVT negative subject""s lower limbs. In other words, the left and right thermograms are thermally similar in posterior or anterior view. By contrast, the thermogram of a DVT affected subject""s lower limb will lack a smooth temperature gradient and, because it is unlikely that both limbs will be positive at the same time, will likely exhibit temperature readings higher than those of the other limb.
It should be noted that, while the process of obtaining a thermogram is largely objective and operator independent, the process of interpreting a thermogram image for the exclusion of DVT is largely subjective, comparable to a physician""s reading of an X-ray. It is therefore a primary object of the present invention to provide a method and apparatus whereby the evaluation of the patient for exclusion of DVT is made entirely objective through automated processing of objectively obtained data.
Although much less expensive than either Doppler ultrasound or venography, thermography typically involves the use of a relatively expensive infrared camera for obtaining the thermogram image. With modern constraints dictating ever more judicious usage of the healthcare dollar, it is necessary to take every opportunity to reduce the cost of patient care while maintaining or exceeding established standard of care. It is therefore another object of the present invention to provide a method and apparatus whereby the cost associated with the exclusion of DVT is reduced without sacrifice in diagnostic reliability.
It is a further object of the present invention to capitalize upon the automated features introduced therewith to increase diagnostic reliability by providing a method and apparatus adaptable for multiple risk factor and/or dynamic analysis.
It is yet another object of the present invention to promote increased patient care by providing a method and apparatus that makes use of disposable components, thereby reducing the risk associated with patient contaminants.
Finally, it is an object of the present invention to provide a method for automated analysis of thermographic data that is useful not only in the apparatus of the present invention but is also extendable for use in the objective analysis of traditionally obtained thermogram images, including those obtained through IR imaging.
In accordance with the foregoing objects, the present inventionxe2x80x94an automated screening tool for the exclusion of deep venous thrombosisxe2x80x94generally comprises a sensor array for gathering of thermal data from the lower limbs of a patient suspected of DVT; a processor for automated analysis of the gathered data; and a display device for reporting the exclusion or non-exclusion of DVT. In the preferred embodiment of the present invention, a microprocessor based system is utilized to control the gathering of thermal data and, thereafter, the reporting of the gathered data to the processor. According to the preferred method for use of the present invention, the gathered thermal data is utilized, alone or in combination with other indicators, as a factor for exclusion of DVT based upon an implemented algorithm.
According to the preferred embodiment of the present invention, a neural network or genetic algorithm is implemented within the processor in order to make an entirely objective determination relative the presence of DVT. This feature makes the present invention particularly adapted to multiple risk factor analysis, wherein factors such as calf circumference; positive Homan sign; colorimetry reading of the limbs; recent surgery or trauma; history of DVT, phlebitic syndrome or venous insufficiency; or presently uncannulated veins may be considered along with thermographic data.
Finally, many other features, objects and advantages of the present invention will be apparent to those of ordinary skill in the relevant arts, especially in light of the foregoing discussions and the following drawings and exemplary detailed description.